Safety paper and preparation thereof



Patented Nov- 21, 1944 L *SAFETY PAPER AND PREPARATION THEREOF Donald T. Jacksonand John L. Parsons, Erie, Pa., assignors to Hammermill Paper Company, Erie, Pa., a corporation of Pennsylvania No Drawing. Application July 22, 1940, Serial No. 346,870

at Claims. (Ci. 117-1) This invention relates to paper that is prepared or treated with a chemical or chemicals designed to form an easily discernible stain on the paper in the event of an attempt to use ink eradicating chemicals to remove writing or ink from the paper. I

Various chemical treatments have been -pro posed for paper to renderit sensitive to ink eradicating chemicals and thus attempt to expose the alteration of matter written in ink on, the paper when it is used for such things as bank checks, drafts, wills or the like.

The majority of the sensitizing chemicals heretofore proposed, however, have had the objection of being rather easily removed from the paper. This enables a person who wishesto alter the writing on the paper to remove the sensitizlng chemical or chemicals before applying. an eradicator to the ink. Water soluble sensitizing chemicals are especially open to this objection since they may be removed before altering the writing on a check or other paper, and thus they do not furnish a telltale stain or other indication of the alteration.

, It is also important in safety paper to have a readily nOticeabIestalndeVeIOp immediately upon the application of ink eradicating chemicals to the paper. Furthermore, the sensitizing chemicals used for thispurpose should be such that they produce a permanent stain that carmot be removed after the stain is formed.- Still other requirement of chemicals used in sensitizing safety paper is that the chemicals be stable to sunlight, ageing and other-exposures to which the paper may be subjected, because if the chemicals lose their staining properties after the paper has been cyclic rings, each such ring containing two hetero atoms, at least one of which is a nitrogen atom, can be incorporated in or on paper to yield a permanent telltale stain of dark character upon the application of an oxidizing agent such as a hypochlorite commonly used in ink eradicators.

While it appears necessary that one of the hetero atoms of the ring be a nitrogen atom, the other hetero atom may be a sulfur atom, in which case the compound would be classed as a thiazine; or another nitrogen atom in which case it would belong to the class of diazines; or an oxygen atom when it would be classed as an oxazine. If the second hetero atom of the ring isfisulfur, it may exist as the sulfide or be associated with oxygen in the form cfa sulfoxide or sulfone. Compounds in which the two hetero atoms occur para to each exposed tcsunlight', or if they produce discoloration of the paper u'pon ageing or exposure to the sunlight, they have little'practical valuefor pur-' P ses of this invention.

'An object of this invention is to provide safety v paper carrying a stable staining chemical that produces a conspicuous and relatively permanent stain upon the application of common ink eradicators to the paper.

Another object is the provision of paperv carr ing'a sensitizing chemical that cannot be readily removed from the paper prior to the application of an ink eradicator thereto without leaving-some indication of the removal.

Another object is to Provide such a safety paper that does not become objectionably discolored upon ageing or exposure to sunlight and that retains this staining property for relatively long periods of time;

Further objects of the invention will be specifically described and will be apparent from the following description of the invention.

We have discovered that certain compounds which contain one or more 6 membered heteroother appear tobe particularly suited for purposes of this invention and such compounds may be represented by the following type formulae:

group or condensed ring structure, and B. may be hydrogen or any suitable substituent therefor.

" We prefer to use compounds in which the same or difierent arylene'o r other suitable carbocyclic ring structures occupy positions 2 and 3, and the Derivatives of thesecompoun'ds positions and 6; respectively. The following are examples of such compounds.

Phenazine Phenoxa'ginc in which one or more additional substituents are substituted in any of the positions susceptible to substitution appear to possess the desirable properties to thegreatest degree for use as a sensitizing agent in or on paper. Also, the salts of any of these compounds capable of forming salts may be used.

These compounds may be incorporated in or on paper to yield a permanent telltale stain of dark charact dizing agent such as hypochlorite commonly used in ink 'eradicators. The stains produced by these compounds are usually dark blue or blue-black, and it is virtually impossible to remove the stain after it is formed without leaving some other mark on the paper that will call attention to the alteration. The stain producing compounds of this invention are relatively insoluble in water and, therefore, cannot easily be removed from the paper prior to the application oi ink eradicator simply by soaking the paper in water. The compounds also have the advantage of not, being substantially affected by a relatively weak acid -solution.which is applied sometimes as a preliminary treatment in the application 01 ink .eradicator.

Ingeneral, the preferred compounds used according to this invention are the substantially colorless, or only slightly colored, light stable thiazines hav the formula ,stituted or unsubstituted arylene or other carbocyclic radicals joined ortho to the nitrogen and sulfur atoms, and It is hydrogen or any suitablevsubstituent such as an acyl, allroxy, alkyl,

m1, alkaryl, aralkyl group. The sulfur may be present as sulfide, or-in combination with oxygen as a sulione or a sulfoxide group. i

One or the simplest dibenzo-, or conjugated cyclic, thiazines is the well known compound phenothiazine, also known as thiodiphenylamine. This compound, although it produces a good stain when oxidized, is slightly sensitive to light, and therefore we prefer to employ the dibenzo-, or conjugated cyclic, thiazines that are substituted in one or more positions by one or more.

substltuents either on one or both of the carer upon the application of an oxibocyclic rings, or Joined dire atom, or both.

Suitable thiazines for purposes of this invention include the substituted thiodiphenylamines,

ctly to the nitrogen thiophenylnaphthylamines, and thiodinaphthylamines or their salts. The following are examples of suitable substituted thiophenylamines, it being understood that other similar substituents m may be used with theother thiodi'arylamines.

s v 01 mol 01 no! N Tetrachlorothiodiphenyiamine 1 NH N 2 4,8-diaminothiodiphenylamine s E1 N-phenylthiodiphenylarnine NHcoom 85 (1 N AH: I

Mtoamino-N-mothylthiodiphenylamin 40 Similarly substituted thiaz i nescontaining one or more monocarbocyclic or polycarbocyclic rings or their substituents or derivatives in place of one or both of the carbocyclic rings or the foregoing compounds may be employed. The thiazines that are used in accor this invention are relatively insoluble in water and generally unaffected by oxalic acid or other acid solutions which might be used in ink eradicators. For this reason, it is very difiicult, if not virtually impossible, to remove these compounds from the paper without making the tampering attempt clearly apparent to the naked eye. These thlazines also'produce very rapidly a deep stain on the paper fibres when subjected to the 55 action 0! an oxidizing agent, and these stains are permanent to such an extent that they cannot be removed without leaving on the paper some mark that calls attention to the altered surface of the paper.

The sensitizing compounds of this invention can be incorporated into the paper or applied as a coating or as an ingredient of a coating thereon, or they may be dissolved in an appropriate solvent and the paper immersed therein. We prefer, however, to add the sensitizing agent, or a so that the chemical will be uniformly embedded in and mixed with the paper fibres making it as difficult as possible to remove the chemical from the paper. It is very convenient to add the sensitizing chemical to the pulp either at the same time or adding the size or at some subsequent stage in the paper making process. In fact, the 76 thiazine type or sensitizing agent may be mixed dance with Q with the sizing material beforeit is mixed with the pulp, thus obtaining a more uniform distribu-' tion of the chemical throughout the pulp. Furthermore, the sensitizing chemical may be mixed withor dispersed in starch or-other commonly used surface or tub sizing materials and applied with these materials in the usual tub sizing operation. Also, water soluble salts or other derivain which R is a substituted or unsubstituted arylene radical attached by two adjacent carbon Y atoms respectively to the nitrogen and X atoms,

R. is hydrogen or a substituent therefor forming a stable material with the balance of the compound, and -x is a substance selected from the group consisting of 8, S0 and S0: with only the tive; .of these sensitizing compounds that react as byhydrolysis or the like to leave the relatively the paper may be insoluble compound in or on employed.

' The proportion of sensitizing chemical may be varied within fairly wide limits, although usually I The term thiazine, is used in the specification and claims in its broad sense to include compounds in which the sulfur atom in the heterocyclic ring may exist as a' sulfide or in an oxidized condition as a sulione or sulfoxide.

The terms and expressions which we have employed are used as terms of description and not oi limitation, and we have no intention. in the use of such terms and expressions, of excluding any equivalentsof the features shown and described or portions thereof, but recognize that various modifications arepossible within the We claim:

scope of the invention claimed.

1. Paper having an agent associated therewith in such a manner as to produce a stain upon the application of an oxidizing reagent to the p per, said agent comprising a light stable substantially colorless organic compound having at least one six membered unsaturated heterocyclic ring containing two hetero atoms disposed para to each other, at least one of said hetero atoms being nitrogen.

2. Paper having an agent associated therewith in such a manner as to produce a stain upon the application of an oxidizing reagent to the paper, said agent comprising a substantially colorless, light stable organic compound having at least one six membered unsaturated heterocyclic rin containing twohetero atoms disposed in the para positions, one of said hetero atoms being nitrogen and the other of said hetero atoms being selected from the class consisting of nitrogen, oxygen and sulfur.

3. Paper having an agent associated therewith in such a manner as to produce a stain upon the application of an oxidizing reagent to the paper, said agent comprising a diarylene heterocyclic compound that is no more than slightly colored having a six membered unsaturated heterocyclic ring containing four carbon atoms, a nitrogen sulfur atom in the ring.

5. Paper having an agent associated in such a manner as to produce a stain upon the application of an oxidizing reagent to the paper, said agent comprising a substantially colorless compound having the formula in which R is a substituted or unsubstituted arylene radical attached by two adjacent carbon atoms respectively to the two nitrogen atoms.

6. Paper having an agent associated therewith in such a manner as'to produce a stain upon the application of an oxidizing reagent to the paper, said agent comprising a substantially colorless compound having the formula in which 1R is a substituted or unsubstituted arylene radical attached by two adjacent carbon atoms respectively to the nitrogen and oxygen, and R is hydrogen or a substituent therefor forming a stable material with the balance of the compound. I

7. Paper having an agent associated therewith in such a manner as to produce astain upon the ap lication of an oxidizing reagent-to the paper,

sa d agent comprising a substantially colorless compound having the formula I k i in which R. is a substituted or unsubstituted atom and a1 second hetero atom para to the nitrogen and selected from. the class consistih of nitrogen, oxygen and sulfur.

4. Paper having an'agent associated therewith insuch a manner as to produce a stain upon the application of an oxidizing reagent to the paper;

said'agent comprising a substantially colorless compound having the formula arylene radical attached by two adjacent carbon atoms respectively to the nitrogen and sulfur, and R. is hydrogen or a substituent therefor forming a. stable material with the balance of the compound. V

8. Paper having an agent associated therewith in such a manner as to produce a stain upon the thiodiphenylamine that is no more than slightly colored.

9. Paper having an agent associatedtherewith insuch a manner as to produce a stain upon the application of an oxidizing reagent to the paper,

said agent comprising a light stable N-substituted thiodiphenylamine.

10. Paper having an agent associated therewith in such a manner as to produce a stain upon the application of an oxidizing reagent to the paper,

therewith stain producing agent.

16. A method of preparing safety paper comprising treating paper with a solution of a light stable substantially colorless organic compound having at least one six membered unsaturated heterocyclic ring containing two hetero atoms para to each other, at least one of said hetero atoms being nitrogen.

17. A method of preparing safety paper comprising incorporating therein a small amount 01 rated heterocyclicwring containing two hetero atoms para to each other, at least one of said hetero atoms being nitrogen.

18. A method 01 preparing safety p p r comprising preparing paper with a small amount of a sensitizing agent incorporated in the surface thereof, said agent comprising a light stable substantially colorless organic compound having at least one six member unsaturated heterocyclic ring containing two hetero atoms para to each other, at least one oi! said hetero atoms being nitrogen.

a sensitizing agent'comprisinga light stable substantially colorless organic compound that forms a more or less permanent stain upon contact with a solution of an oxidising agent, said compound having at least one six membered unsatu- 19. Paper having an agent associated therewith in such a manner as to produce a. stain upon the application of an oxidizing reagent to the paper,

said agent. being present in an amount of from 0.25 to 2% 01 the paper by weight and comprisin a light stable substituted thiodiphenylamine that is no more than slightly colored.

20. Paper having an agent associated therewith in such a manner as to produce a stain upon the application of an oxidizing reagent to the paper, said agent being present in an amount of from 0.25 to 2% of the paper by weight and comprising a light stable N-substituted thiodiphenylamine.

DONALD T. JACKSON. JOHN L. PARSONS. 

